1. Field of the Invention
The present invention relates to an ultrasonic flow meter which measures the flow rate of a liquid which is flowing in a conduit or the like by using ultrasonic waves.
Priority is claimed on Japanese Patent Application No. 2003-176421, filed Jun. 20, 2003, the content of which is incorporated herein by reference.
2. Description of the Related Art
As a flow meter which measures the flow rate of a liquid which is flowing through a conduit, there is a per se known type of ultrasonic flow meter which utilizes ultrasonics.
In this ultrasonic flow meter, there is provided, in a conduit for measurement of the flow of the flowing liquid, a measurement section which comprises transducers spaced apart by an interval in the longitudinal direction. An ultrasonic pulse which is generated from a first one of these transducers is received by another of these transducers, and further an ultrasonic pulse which is generated from that other one of these transducers is received by the first one thereof, so that the speed of the flow of the liquid within the conduit for measurement may be obtained from the difference of the transmission times for these ultrasonic pulses; and the flow rate is measured from this flow velocity.
As a conventional ultrasonic flow meter, for example, there is a per se known prior art (refer to Japanese Patent Application, First Publication No. Sho 61-132823) in which two ring shaped transducers are fitted in the flow conduit at a suitable interval so that each of their central axes matches the central axis of the flow conduit, with their central open portions being of almost the same size as the diameter of the flow conduit, and moreover with each of these ring shaped portions having a width equal to or greater than the thickness of the flow conduit. In this type of transducer, when an electrical signal of a predetermined frequency is applied to one of these ring shaped transducers, the transducer oscilates in its radial direction, so that, an ultrasonic signal is symmetrically emitted along the direction of the central axis of this transducer, which is the direction of the flow conduit. This ultrasonic signal passes through the central open portion of the other ring shaped element and oscilates it, and then an electrical signal which corresponds to the ultrasonic signal is outputted.
With such a prior art type of ultrasonic flow meter, when the conduit for measurement in to which both ends of the measurement section are fixed is oscilated due to reception of some unintentional external force such as noise or the like, then, when the oscilations are emitted from the transducer for measuring the flow rate of the flowing liquid, these oscilations become mixed with the oscilations of the conduit for measurement which the measurement device has received from externally, and therefore, the problem arises that it may become impossible to measure the flow rate of the flowing liquid accurately with the transducers, due to the ultrasonic signal which is being inputted from the transducer as a measurement oscilation becoming superimposed with these oscilations from externally. This fact becomes a particularly severe problem when the conduit for measurement is made from a synthetic resin material, since such a conduit for measurement is not a rigid body.
The present invention has been conceived in the light of the above described situation, and its objective is to provide an ultrasonic flow meter which can measure the flow rate of a flowing liquid accurately, by suppressing oscilations of the conduit for measurement which are received from externally.